Process of producing a superconducting magnet made of a high-temperature bulk superconductor

ABSTRACT

There is established a superconducting magnet made of a high-temperature bulk superconductor and capable of trapping a high magnetic field with ease and stably. The superconducting magnet made of the high-temperature bulk superconductor, for use by trapping a magnetic field, is made of the bulk superconductor with an artificial hole therein, a low-melting metal impregnated into, and filling up at least the artificial hole, and a heat-conducting metal material embedded in portions of the high-temperature bulk superconductor, impregnated with, and filled with the low-melting metal. The superconducting magnet can be produced by a process involving the steps of providing the artificial hole in the high-temperature bulk superconductor, disposing the heat-conducting metal material in at least the artificial hole, applying a process of impregnating and filling up at least the artificial hole with the low-melting metal, and subsequently, executing a process of magnetizing.

This is a division of Ser. No. 10/454,723, filed Jun. 4, 2003 now U.S.Pat. No. 7,046,110.

FIELD OF THE INVENTION

The present invention relates to a superconducting magnet made of ahigh-temperature bulk superconductor which is capable of securing a hightrapped magnetic field in a relatively short time and a process ofproducing the same, and the invention is expected to make a greatcontribution to enhancement of technology in application fields, such asa magnetic levitation train, superconducting bearings for use inflywheel energy storage, and a magnetic separation apparatus, whereinutilization of the high-temperature bulk superconductor, under a highelectromagnetic force, is desired.

BACKGROUND OF THE INVENTION

Following discovery of oxide superconducting materials having arelatively high critical temperature (Tc) such as LiTi₂O₃, Ba(Bi, Pb)O₃,and (Ba, K)BiO₃, there have lately been developed copper oxidesuperconducting materials one after another, such as (La, Sr)₂CuO₄,REBa₂Cu₃O₇ (RE: rare earth element), Bi₂Sr₂Ca₂Cu₃O₁₀, Ti₂Ba₂Ca₂Cu₃O₁₀,and HgBa₂Ca₂Cu₃O₈ having still higher critical temperatures.

Incidentally, it has been known that although a superconducting materialhaving a higher critical current density in comparison with an ordinaryconducting material can pass a large electric current without loss asdescribed above, there is a risk of the superconducting material beingdestroyed depending upon its strength in the case where such a largeelectric current is passed therethrough because a large electromagneticforce acts on superconductors.

Further, as a result of recent improvement in the characteristics of ahigh temperature bulk superconductor (particularly, a copper oxidesuperconductor) and recent trends for larger sizes thereof, themagnitude of a magnetic field that can be trapped in a bulksuperconductor has increased by leaps and bounds. Such an increase inthe magnitude of the magnetic field is accompanied by an increase in theelectromagnetic force acting on the bulk superconductors, so that therehas lately arisen a problem in that restriction is inevitably imposed ona trapped magnetic field depending on the strength of a bulksuperconductor. Accordingly, for enhancement in performance of a bulksuperconducting magnet-utilizing a trapped magnetic field, it has becomeimportant to enhance the mechanical properties of the bulksuperconductors rather than to further enhance the superconductingproperties.

Accordingly, the inventor, et al. have previously proposedhigh-temperature bulk superconductors, having a considerably highmechanical strength, as follows:

-   a) an “oxide superconductor” (refer to JP 3144675 B) comprising an    oxide bulk superconductor produced by a melt process and having a    resin-impregnated layer of an epoxy resin, and so forth    (resin-impregnated layer impregnated with resin through microcracks    and voids unavoidably included therein in a process of producing an    oxide bulk superconductor in the state of a pseudo single crystal in    an atmosphere under a reduced pressure);-   b) an “oxide superconductor” (refer to JP 3144675 B) comprising an    oxide bulk superconductor having a resin-impregnated layer and    produced by a melt method, wherein the oxide bulk superconductor    contains at most 40% by weight of Ag;-   c) an “oxide superconductor” (refer to JP 3100370 B) comprising an    oxide bulk superconductor having a resin-impregnated layer and the    outer surface thereof covered with a resin layer dispersedly    incorporating a filler material of a small linear thermal expansion    coefficient, such as quartz, calcium carbonate, alumina, alumina    hydrate, glass, talc, calcined gypsum, and so forth, produced by a    melt process;-   d) an “oxide superconductor” (refer to JP 3100375 B) comprising an    oxide bulk superconductor having “an adhesively covering layer of    resin-impregnated fabric” on the outer surface thereof and a    resin-impregnated layer in a surface portion thereof, produced by a    melt process; and so forth.

The above-described oxide superconductors (high-temperature bulksuperconductors) with such a treatment of forming the resin-impregnatedlayer, applied thereto, have an excellent mechanical strength andconsequently, have excellent characteristics in that they are capable ofensuring a high trapped magnetic field (high trapped magnetic field withthe magnitude thereof enhanced to the extent in excess of 10 T in termsof magnetic flux density), which has not been seen before, and besides,deterioration of the trapped magnetic field is small, even after thermalcycles of cooling and warming, and electromagnetic hysteresis ofelectromagnetic force repeatedly applied thereto. As a result of furtherperusal thereof by the inventor, et al, however, it has become apparentthat even those high-strength high-temperature bulk superconductors havethe following problems.

More specifically, with a superconducting magnet made of thehigh-temperature bulk superconductor, there is normally adopted amagnetizing method of applying a magnetizing treatment to thehigh-temperature bulk superconductor placed in an external magneticfield higher than a trapped magnetic field aimed as a target whilecooling the same with a gas evolved from liquid helium, and causing amagnetic field to be sufficiently trapped by gradually lowering theexternal magnetic field from the state described. In such a case, therewill not occur a situation such that the high-temperature bulksuperconductor reinforced by resin-impregnation, or the like is unableto withstand Lorentz force when an external magnetic field with amagnetic flux density in excess of 10 T is applied, as with the case ofa conventional high-temperature bulk superconductor withoutreinforcement by resin-impregnation, or the like, thereby resulting indestruction. In the case of applying the external magnetic field withthe magnetic flux density in excess of 10 T, as never experiencedbefore, a phenomenon (quenching phenomenon) wherein a superconductingstate is broken by generation of heat due to an avalanche-like movementof magnetic flux lines, called the flux jump, is prone to occur.

The higher a magnetic field becomes, the more often such a phenomenon,as observed when applying a magnetizing treatment to thehigh-temperature bulk superconductor, is prone to occur, and in the caseof a magnetic field with a magnetic flux density in excess of 10 T, ithas been found extremely difficult to magnetize even thehigh-temperature bulk superconductor with the reinforcing treatmentapplied thereto due to the above-described phenomenon.

That is, the inventors have found through experiments on thehigh-temperature bulk superconductor reinforced by resin-impregnationthat in order to attain a higher trapped magnetic field in thehigh-temperature bulk superconductor, there is the need for avoidingadverse effects of generation of heat, due to the flux jump, in additionto the need for enhancement in mechanical strength of thehigh-temperature bulk superconductor.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a superconductingmagnet made of a high-temperature bulk superconductor, capable oftrapping a high magnetic field with ease and stably, therebycontributing to a further enhancement in the performance of equipmentand so forth with the superconducting magnet applied thereto.

Accordingly, in order to achieve the object described above, theinventor, et al. have conducted intensive studies and have succeeded inobtaining the following information.

The quenching phenomenon, occurring at the time of applying themagnetizing treatment to the high-temperature bulk superconductor, asdescribed above, is attributable to “generation of heat” caused byelectromotive voltage generated by rapid movement (the flux jump) ofmagnetic flux lines, passing through the high-temperature bulksuperconductor, to the periphery thereof, and because of a low thermalconductivity of the high-temperature bulk superconductor, heat locallygenerated cannot be dissipated to the outside of the high-temperaturebulk superconductor, so that accumulation of the heat causes thetemperature of the bulk superconductor to rise locally, therebyresulting in quenching.

In contrast, if an artificial hole (either a through-hole or a bottomedhole) is bored at a suitable location of an oxide bulk superconductor,and the hole is brought into contact with a low-melting metal (alow-melting metal having a melting point not higher than from 200° C. to300° C.) in a molten state, the oxide bulk superconductor is impregnatedwith the low melting metal through microcracks and voids, existing inthe surface of the oxide bulk superconductor and in the interior thereof(in spite of the tendency of impregnation with the low-melting metalbeing considered unlikely to occur, it is in fact difficult to preventpresence of the microcracks and voids inside the oxide bulksuperconductor in the production process thereof, so that impregnationof the low-melting metal into the oxide bulk superconductor isaccomplished through the microcracks and voids by a vacuum drawingtreatment and so forth) and at the same time, the artificial hole in astate of being linked with layers impregnated with the low melting metalis filled with the low-melting metal.

With the oxide bulk superconductor impregnated with, and filled with thelow-melting metal, even if there occurs local generation of heat due tothe flux jump at the time of applying the magnetizing treatment thereto,the heat rapidly propagates to the artificial hole impregnated with, andfilled with the low-melting metal through the layers impregnated withthe low melting metal having an excellent thermal conductivity becauseit is metal, so that there emerges no spot where an extreme rise intemperature occurs, thereby blocking the occurrence of quenching.

In addition, with the oxide bulk superconductor impregnated with, andfilled with the low-melting metal, the mechanical strength thereof isenhanced and a tendency of cracking can be largely reduced.

In this case, by embedding a heat-conducting metal material such as, analuminum wire with the low-melting metal filled in, and solidified inthe artificial hole, the heat generated inside the oxide bulksuperconductor can be released to the outside more rapidly, so that itbecomes possible to cause the oxide bulk superconductor to trap a highmagnetic field by a magnetizing process in a relatively short processingtime.

The invention has been developed based on the above-describedinformation and findings, and provides a superconducting magnet made ofa high-temperature bulk superconductor, and a process of producing thesame, as shown under the following items (1) through (4).

-   (1) A superconducting magnet made of a high-temperature bulk    superconductor, for use by trapping a magnetic field, wherein the    high-temperature bulk superconductor is provided with an artificial    hole, at least the artificial hole is impregnated with, and filled    with a low-melting metal, and a heat-conducting metal material is    embedded in portions of the high-temperature bulk superconductor,    which is impregnated with, and filled with the low-melting metal.-   (2) A superconducting magnet made of a high-temperature bulk    superconductor as set forth under item (1) above, wherein the heat    conducting metal material is made of an element selected from the    group consisting of Al, Cu, Ag, and Au.-   (3) A process of producing a superconducting magnet made of a    high-temperature bulk superconductor, comprising the steps of    providing an artificial hole in the high-temperature bulk    superconductor, disposing a heat-conducting metal material in at    least portions of the high-temperature bulk superconductor where    bonding of the heat conducting metal material with a low-melting    metal to be impregnated in, and filling up at least the artificial    hole is to be made before impregnating and filling up at least the    artificial hole with the low-melting metal, and executing a process    of magnetizing the high-temperature bulk superconductor to which the    heat-conducting metal material is embedded through the intermediary    of the low melting metal after being solidified.-   (4) A process of producing a superconducting magnet made of a    high-temperature bulk superconductor as set forth under item (3)    above, wherein the process of magnetizing is executed with an    external magnetic field maintaining a magnetic flux density not less    than 10 T.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic sectional view of an embodiment of asuperconducting magnet made of a high-temperature bulk superconductoraccording to the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

Now, any kind selected from among the known oxide bulk superconductorsmay be used as an oxide bulk superconductor applicable to the presentinvention, but it can be said that an RE-Ba—Cu—O based copper oxide bulksuperconductor (RE refers to at least one rare earth element selectedfrom the group consisting of Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, andYb) known as a high-temperature oxide superconducting material having ahigh trapped magnetic field is preferably used for the purpose.

Particularly, more preferable for use as the oxide bulk superconductoris an oxide superconducting material comprising an REBa₂Cu₃O_(y) phase(RE refers to at least one rare earth element selected from the groupconsisting of Y, Dy, Ho, Er, Tm, and Yb) known as a material having ahigh trapped magnetic field as a parent phase, and an RE₂BaCuO₅ phase(RE refers to at least one rare earth element selected from the groupconsisting of Y, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb) as a dispersionphase, in an amount of at most 50% by volume of the parent phase, and anoxide superconducting material comprising an RE_(1+x)Ba_(2-x)Cu₃O_(y)phase (RE refers to at least one rare earth element selected from thegroup consisting of La, Nd, Sm, Eu, and Gd, and preferably, with−0.1<x<0.2, and 6.5<y<7.2) as a parent phase, and anRE_(4-2x)Ba_(2+2x)Cu_(2-x)O_(10-2x) phase (RE refers to at least onerare earth element selected from the group consisting of La, and Nd, andpreferably, with −0.2<x<0.3) or an RE₂BaCuO₅ phase (RE refers to atleast one rare earth element selected from the group consisting of Sm,Eu, and Gd) as a dispersion phase, in an amount of at most 50% by volumeof the parent phase.

It can be said that “the oxide superconductor having theresin-impregnated layer” disclosed in JP 3144675 B, “the oxidesuperconductor having the resin-impregnated layer, and the outer surfacethereof, covered with a resin layer dispersedly incorporating a fillermaterial of a small linear thermal expansion coefficient”, disclosed inJP 3100370 B), “the oxide superconductor having the adhesively coveringlayer of the resin-impregnated fabric on the outer surface thereof or“the oxide superconductor having the resin-impregnated layer in thesurface portion thereof and the outer surface thereof covered with theadhesive covering layer of the resign-impregnated fabric”, as disclosedin refer to JP 3100375 B is preferably used for the oxide bulksuperconductor described above.

The position and number of artificial holes to be provided in ahigh-temperature bulk superconductor may be decided upon as appropriate,but it is normally sufficient to provide one hole in the central partthereof.

The artificial hole may be either a through-hole or a bottomed hole andmeans of forming the artificial hole are not to be particularlyspecified, however, making a hole by a drill is considered as theeasiest and preferable means.

Because the oxide bulk superconductor causes bound oxygen to dissipatewhen heated above a certain temperature, failing to exhibitsuperconductivity, there is a need for employing a metal or an alloyhaving a melting point lower than “a temperature causing the dissipationof oxygen”, as a low melting metal to be impregnated in, and filling upthe artificial hole.

Further, “the temperature causing the dissipation of oxygen” is on theorder of about 300° C. in the case of a Y—Ba—Cu—O based bulksuperconductor, on the order of about 250° C. in the case of aGd—Ba—Cu—O based bulk superconductor, and on the order of about 200° C.in the case of an Sm—Ba—CU-O based bulk superconductor or Nd—Ba—Cu—Obased bulk superconductor. Accordingly, any low melting metal having amelting point not higher than 200° C. can be applied to any kind ofoxide bulk superconductor.

In this connection, there are shown hereunder specific examples of thelow-melting metals applicable to the invention and respective meltingtemperatures thereof.

-   (a) 44.7 wt. % Bi-22.6 wt. % Pb-8.3 wt. % Sn-5.3 wt. % Cd-19.1 wt. %    In alloy (melting temperature: 46.7° C.)-   (b) 42.34 wt. % Bi-22.86 wt. % Pb-11.0 wt. % Sn-8.46 wt. % Cd-15.34    wt. % In alloy (melting temperature: 47.0° C.)-   (c) 49.4 wt. % Bi-18.0 wt. % Pb-11.6 wt. % Sn-21.0 wt. % In alloy    (melting temperature: 58.0° C.)-   (d) 48.0 wt. % Bi-25.6 wt. % Pb-12.8 wt. % Sn-9.6 wt. % Cd-4.0 wt. %    In alloy (melting temperature: 61.0° C.)-   (e) 50.0 wt. % Bi-25.0 wt. % Pb-12.5 wt. % Sn-12.5 wt. % Cd alloy    (melting temperature: 60.0° C.)-   (f) 50.0 wt. % Bi-26.7 wt. % Pb-13.3 wt. % Sn-10.0 wt. % Cd alloy    (melting temperature: 70.0° C.)-   (g) 40.0 wt. % Bi-40.0 wt. % Pb-11.5 wt. % Sn-10.0 wt. % Cd alloy    (melting temperature: 70.0° C.)-   (h) 57.0 wt. % Bi-17.0 wt. % Sn-26.0 wt. % In alloy (melting    temperature: 78.8° C.)-   (i) 51.65 wt. % Bi-40.2 wt. % Pb-8.15 wt. % Cd alloy (melting    temperature: 91.5° C.)-   (j) 52.5 wt. % Bi-32.0 wt. % Pb-15.5 wt. % Sn alloy (melting    temperature: 95.0° C.)-   (k) 52.5 wt. % Bi-32.0 wt. % Pb-15.5 wt. % Sn alloy (melting    temperature: 95.0° C.)-   (l) 50.0 wt. % Bi-28.0 wt. % Pb-22.0 wt. % Sn alloy (melting    temperature: 100° C.)-   (m) 53.9 wt. % Bi-25.9 wt. % Sn-20.2 wt. % Cd alloy (melting    temperature: 102.5° C.)-   (n) 55.5 wt. % Bi-44.5 wt. % Pb alloy (melting temperature: 124° C.)-   (o) 58.0 wt. % Bi-42.0 wt. % Sn alloy (melting temperature: 138° C.)-   (p) 40.0 wt. % Bi-60.0 wt. % Sn alloy (melting temperature: 138° C.)-   (q) 50.0 wt % Bi-27.5 wt % Pb-13.5 wt. % Sn-9.0 wt. % Sb alloy    (melting temperature: 148° C.)-   (r) Bi (melting temperature: 271.3° C.)-   (s) In (melting temperature: 156.2° C.)-   (t) Sn (melting temperature: 231.9° C.)

It can be said that wire made of any element selected from the groupconsisting of Al, Cu, Ag, Au, and so forth, having a high thermalconductivity, is preferably used for a heat-conducting metal materialfor allowing heat to escape from a portion of the low-melting metal,impregnated in, and filling up the artificial hole, to the outside, butthe heat-conducting metal material is not particularly limited thereto,so that any metal material having an excellent thermal conductivity maybe used. For example, when impregnating and filling up the artificialhole with a low-melting metal in a molten state, the low-melting metalmay be caused to form a covering layer so as to cover the surface of thehigh-temperature bulk superconductor, enabling the covering layer of thelow-melting metal to play also a role of the heat-conducting metalmaterial.

A method of bringing at least a region of the artificial hole of theoxide bulk superconductor kept in an atmosphere under reduced pressure,such as in a vacuum, into contact with the low-melting metal in a moltenliquid state is preferable as a process for impregnating and filling theartificial hole of the oxide bulk superconductor with the low-meltingmetal, however, other methods, such as “a pressure impregnation method”and so forth, may also be used without any problems.

In this connection, it is preferable to carry out in this stage ofprocessing the impregnation of the low-melting metal not only into theregion of the artificial hole but also from the entire surface of theoxide bulk superconductor.

Upon bringing the oxide bulk superconductor into contact with thelow-melting metal in a molten state in an atmosphere under reducedpressure or in a pressurized atmosphere, portions of the low-meltingmetal permeate into the oxide bulk superconductor through microcracksand voids, having respective openings in the surface of the oxide bulksuperconductor (including the inner surface of the artificial hole),fill up the microcracks and voids existing inside the oxide bulksuperconductor (particularly, in the surface portion thereof), and thoseportions of the low-melting metal are united with a portion of thelow-melting metal, filling up the artificial hole, to be therebystrongly bonded with the oxide bulk superconductor. Accordingly, localheat generated at the time of magnetizing is rapidly dissipated to theportion of the low-melting metal filling the artificial hole, throughthe portions of the low melting metal impregnated into the oxide bulksuperconductor.

In this connection, it is to be pointed out that impregnation of thelow-melting metal will not occur by a process of simply bringing theoxide bulk superconductor into contact with the low-melting metal in amolten state instead of the process of impregnation in an atmosphereunder a reduced pressure or the process of pressure impregnation, andsolidified portions of the low-melting metal will not satisfactorilybond with the oxide bulk superconductor, thereby failing to exhibitdesired effects of heat dissipation.

There is no limitation on the means for bonding the portion of thelow-melting metal, impregnated in, and filling up the artificial hole,with the heat-conducting metal material as long as smooth heatconduction is attained, however, it is preferable to employ a method ofinserting the heat-conducting metal material, such as an aluminum wire,in the artificial hole provided in the high-temperature bulksuperconductor so as to be disposed therein before applying a process ofimpregnation with the low-melting metal when impregnating and filling upthe artificial hole with the low-melting metal, and solidifying theportion of the low-melting metal, in the artificial hole, so as to beintegral with the heat conducting metal material.

FIG. 1 is a schematic sectional view of an embodiment of asuperconducting magnet made of a high-temperature bulk superconductoraccording to the invention.

The superconducting magnet made of the high-temperature bulksuperconductor is obtained by boring an artificial through-hole in thehigh-temperature bulk superconductor formed in the shape of a disk,inserting a heat-conducting metal wire (an aluminum wire) with both endssplit in the shape resembling the arms of an octopus into the artificialthrough-hole, and subsequently applying the process of impregnation withthe low-melting metal to the high-temperature bulk superconductor inwhole, including the artificial through-hole.

As shown in FIG. 1, because there exist numerous microcracks and voidsin the high-temperature bulk superconductor formed as above, if theprocess of impregnation with the low melting metal is applied in anatmosphere under a reduced pressure, and so forth, the low-melting metalis impregnated into the microcracks and voids while filling up theartificial through-hole and fully covering the surface of thehigh-temperature bulk superconductor, thereby being bonded and unitedwith the heat-conducting metal wire before solidification.

Accordingly, local heat generated at the time of magnetizing rapidlypropagates to the portion of the low-melting metal, filling up theartificial hole, through the portions of the low-melting metalimpregnated, and is transferred to a covering layer of the low-meltingmetal, covering the surfaces of the high-temperature bulksuperconductor, to be thereby diverted to the outside. Hence, occurrenceof a phenomenon leading to quenching due to a rise in temperature atlocalized parts of the high-temperature bulk superconductor can beeffectively blocked.

FIG. 1 shows an example of the superconducting magnet made of thehigh-temperature bulk superconductor, wherein both ends of theheat-conducting metal wire are bonded with the covering layer of the lowmelting metal, covering the surfaces of the high-temperature bulksuperconductor, respectively, however, both the ends of theheat-conducting metal wire may obviously be bonded with other heatdissipating members.

For a process of magnetizing a superconducting magnet made of thehigh-temperature bulk superconductor, it is preferable to adopt apublicly known method, that is, the magnetizing method of applying ahigh external magnetic field in a gas evolved from liquid helium tothereby trap a magnetic field, however, it can be said that by applyinga magnetizing process with the external magnetic field having a magneticflux density in excess of 10 T, the invention will have more pronouncedadvantageous effects.

Further, it goes without saying that either “a static magnetic fieldmethod” or “a pulse method” may be adopted as a magnetizing method.

Now, the invention is described in more detail with reference to workingexamples.

Example 1

Bulk materials comprising a YBa₂Cu₃O_(y) superconductor and a Y₂BaCuO₅phase dispersed therein, in an amount of 0, 10, 20, 30, and 40% byvolume, were prepared by a melt process.

MYBa₂Cu₃O_(y) material with an SmBa₂Cu₃O_(y) crystal as a seed crystalwas cooled down to 1050° C. in 30 minutes after heating at 1100° C. for20 minutes, and subsequently, was further cooled down to 900° C. at acooling rate of 0.5° C./h.

After crystal growth, oxygen annealing was applied thereto in an oxygenflow at 400° C. under one atmospheric pressure for 250 hours.

Next, respective bulk superconductors were placed in a vacuum container,and were permeated with a resin by the following method of resinimpregnation.

That is, in a preprocess stage, the respective bulk superconductors wereimmersed in a silane-based coupling agent {R′ Si (OR)₃: R′ is an organicfunctional group, and OR is an inorganic functional group} and were putin a vacuum tank so as to be in a condition of a reduced pressure at6.7×10⁻² Pa, subsequently, reverting to a condition under atmosphericpressure. Then, the respective bulk superconductors were put in a dryingfurnace to be dried.

Subsequently, bisphenol A epoxy resin, an aromatic polyamine, and asilane-based coupling agent, in a condition preheated up to 30° C.,respectively, were mixed at a blending composition (weight ratio) of100:32:1, and were deaerated in a vacuum. Thereafter, the respectivebulk superconductors were preheated up to 70° C., and were put in avacuum tank where the pressure was reduced to 6.7×10⁻² Pa. Subsequently,the resin was poured in such a way as to cover the respective bulksuperconductors, the pressure was increased up to 0.4 MPa, and heatingwas applied thereto below 80° C. for 6 hours and below 120° C. for 2hours, thereby curing the resin.

An artificial through-hole (1 mm in diameter) was bored in therespective bulk superconductors, impregnated with the epoxy resin, usinga drill. The through-hole was provided in the central part of therespective bulk superconductors, in the direction of the c-axis thereof.

Subsequently, the same treatment with the silane-based coupling agent asdescribed above was applied thereto, an aluminum bar (a soft wire-likebar 0.9 mm in diameter) was inserted into the artificial through-hole asbored, and an end of the aluminum bar, protruding into a bottom part ofthe respective bulk superconductors (on the side where the seed crystaldid not exist) was split into two parts to be brought into intimatecontact with the bottom surface of the respective bulk superconductors.

The respective bulk superconductors were preheated up to 150° C., aliquid metal having a chemical composition of 53.9% Bi-25.9. % Sn-20.2%Cd also at 150° C. was poured so as to accumulate at the bottom of therespective bulk superconductors, and pressure was reduced to 6.7×10⁻² Pain the vacuum tank to be subsequently increased up to 0.4 MPa.Thereafter, the temperature was lowered down to normal temperature (20°C.), thereby solidifying the liquid metal.

Subsequently, the respective bulk superconductors with carbon fiberwound around the circumferential side face thereof were impregnated withresin by the same method as described above.

Next, the respective bulk superconductors were cooled down to 100K, amagnetic field with a magnetic flux density of 13 T was applied thereto,the respective bulk superconductors were further cooled down to 50K, andsubsequently, a magnetic field on the respective surfaces of the bulksuperconductors was measured by use of a Hall sensor device whilelowering the magnetic field from 13 T.

As a result, the specimens having a content of Y211 phase at 0, 10, 20,30, and 40%, trapped magnetic flux densities of 5 T, 7 T, 6.5 T, 6 T,and 6 T, respectively.

On the other hand, when the same measurements as described above wereconducted on specimens wherein a vacuum treatment with a low-meltingmetal was not applied after providing an artificial hole, it was foundthat after the temperature of the bulk superconductors rose up to 55K inthe course of lowering a magnetic field, there was a sudden increase intemperature up to 70K. It was confirmed that the trapped magnetic fieldsshowed magnetic flux density values close to 0 T.

As described in the foregoing, with all the specimens in which thetreatment of impregnation with the low-melting metal was applied afterproviding the artificial hole, relatively large trapped magnetic fieldswere obtained as compared with the specimens to which such treatment wasnot applied.

Further, it was found by post-test observation with a microscope thatthe interior of the artificial hole was filled with the low-meltingmetal and internal microcracks in the vicinity of the artificial holewere also filled with the low melting metal.

Example 2

Respective bulk materials comprising an Sm_(0.9)Ba_(2.1)Cu₃O_(y) oxidesuperconductor having an Sm₂BaCuO₅ phase (Sm211 phase) dispersedtherein, in an amount of 30, and 40% by volume, respectively, wereprepared by the melt process. Melting conditions were adopted such thatthe Sm_(0.9)Ba_(2.1)Cu₃O_(y) material was cooled down to 1050° C. in 20minutes after heating at 1200° C. for 20 minutes in an atmosphere of amixed gas of oxygen and argon with an oxygen partial pressure maintainedat 1% and subsequently was further cooled down to 900° C. at a coolingrate of 0.5° C./h after placing an NdBa₂Cu₃O_(y) crystal on top as aseed crystal.

With respect to specimens containing 0%, and 10% of the Sm211 phase,respectively, in a post-growth stage, large cracks were observed.Further, even with specimens containing 20% of the Sm211 phase,microcracks were observed although not observed by the naked eye.

Thereafter, oxygen annealing was applied to respective bulksuperconductors containing 30%, and 40% of the Sm211 phase without anycracks being observed, in an oxygen flow at 350° C. under oneatmospheric pressure for 200 hours.

Next, the respective bulk superconductors were placed in a vacuumcontainer and the respective bulk superconductors were permeated withresin by the following method of resin impregnation.

That is, in a preprocess stage, the respective bulk superconductors wereimmersed in a silane-based coupling agent {R′ Si (OR)₃: R′ is an organicfunctional group, and OR is an inorganic functional group}, and were putin a vacuum tank so as to be in a condition of a reduced pressure at6.7×10⁻² Pa, subsequently reverting to a condition under atmosphericpressure. Then, the respective bulk superconductors were put in a dryingfurnace to be dried.

Subsequently, bisphenol A epoxy resin, an aromatic polyamine, and asilane-based coupling agent, in a condition preheated up to 30° C.,respectively, were mixed at a blending composition (weight ratio) of100:32:1. Thereafter, the respective bulk superconductors were preheatedup to 70° C., the resin was poured in such a way as to cover therespective bulk superconductors, and the respective bulk superconductorswere put in the vacuum tank where the pressure was reduced to 6.7×10⁻²Pa to then be deaerated.

After sufficiently eliminating the pores, the pressure was increased upto 0.3 MPa, and heating was applied thereto below 80° C. for 6 hours andbelow 120° C. for 2 hours, thereby curing the resin.

An artificial through-hole (1 mm in diameter) was bored in therespective bulk superconductors, impregnated with the epoxy resin, usinga drill. The through-hole was provided in the central part of therespective bulk superconductors, in the direction of the c-axis thereof.

Subsequently, with the same treatment with the silane-based couplingagent as described above applied thereto, an aluminum bar (a softwire-like bar 0.9 mm in diameter) was inserted into the artificialthrough-hole as bored, and an end of the aluminum bar, protruding into abottom part of the respective bulk superconductors (on the side wherethe seed crystal did not exist) was split into two parts to be broughtinto intimate contact with the bottom surface of the respective bulksuperconductors.

The respective bulk superconductors were preheated up to 150° C., aliquid metal having a chemical composition of 53.9% Bi-25.9. % Sn-20.2%Cd at 120° C. was poured so as to accumulate at the bottom of therespective bulk superconductors, and the pressure was reduced to6.7×10⁻² Pa in the vacuum tank to be subsequently increased up to 0.4MPa. Thereafter, the temperature was lowered down to normal temperature(20° C.), thereby solidifying the liquid metal.

Subsequently, the respective bulk superconductors with carbon fiberwound around the circumferential side face thereof were impregnated withresin by the same method as described above.

Next, the respective bulk superconductors were cooled down to 100K, amagnetic field with a magnetic flux density at 13 T was applied thereto,the respective bulk superconductors were further cooled down to 50K, andsubsequently, a magnetic field on the respective surfaces of the bulksuperconductors was measured by use of the Hall sensor device whilelowering the magnetic field from 13 T.

As a result, the specimens having a content of the Sm211 phase at 30%,and 40% trapped magnetic flux densities at a high value of 10 T, and 8T, respectively.

On the other hand, when the same measurements as described above wereconducted on specimens in which vacuum treatment with a low meltingmetal was not applied after providing an artificial hole, it was foundthat after the temperature of bulk superconductors rose up to 55K in thecourse of lowering a magnetic field, there was a sudden increase intemperature up to 90K. It was confirmed that the trapped magnetic fieldsshowed magnetic flux density values close to 0 T.

As described in the foregoing, with all the specimens whereinimpregnation with the low melting metal was applied after providing theartificial hole, relatively large trapped magnetic fields were obtainedas compared with the specimens to which such treatment was not applied.

Further, it was found by post-test observation with a microscope thatthe interior of the artificial hole was filled with the low meltingmetal and internal microcracks in the vicinity of the artificial holewere also filled with the low melting metal.

Example 3

Respective bulk materials comprising an Nd_(0.9)Ba_(2.1)Cu₃O_(y) oxidesuperconductor and an Nd_(3.6)Ba_(2.4)Cu_(1.8)O_(z), phase (Nd422 phase)dispersed therein, in an amount of 0, 10, 20, 30, and 40% by volume,were prepared by the melt process.

Melting conditions were adopted such that Nd_(0.9)Ba_(2.1)Cu₃O_(y)material (with an MgO single crystal on top as a seed crystal) wascooled down to 1010° C. in 20 minutes after heating at 1040° C. for 20minutes in “an atmosphere of a mixed gas of oxygen and argon with anoxygen partial pressure maintained at 0.1%”, and subsequently, wasfurther cooled down to 900° C. at a cooling rate of 0.5° C./h.

With respect to specimens containing 0%, and 10% of the Nd422 phase, ina post-growth stage, large cracks were observed.

Thereafter, oxygen annealing was applied to respective bulksuperconductors containing 20%, 30%, and 40% of the Nd422 phase, in anoxygen flow at 300° C. under one atmospheric pressure for 300 hours. Nocracks were observed for these specimens.

Next, the respective bulk superconductors were placed in a vacuumcontainer, and the respective bulk superconductors were permeated withresin by the following method of resin impregnation.

That is, in a preprocess stage, the respective bulk superconductors wereimmersed in a silane-based coupling agent {R′ Si (OR)₃: R′ is an organicfunctional group, and OR is an inorganic functional group}, and were putin a vacuum tank so as to be in a condition of a reduced pressure at6.7×10⁻² Pa, subsequently, reverting to a condition under atmosphericpressure. Then, the respective bulk superconductors were put in a dryingfurnace to be dried.

Subsequently, bisphenol A epoxy resin, an aromatic polyamine, and asilane-based coupling agent, in a condition preheated up to 30° C.,respectively, were mixed at a blending composition (weight ratio) of100:32:1, and were deaerated in a vacuum. Thereafter, the respectivebulk superconductors were preheated up to 70° C. and were put in thevacuum tank where the pressure was reduced to 6.7×10⁻² Pa. Subsequently,the resin was poured in such a way as to cover the respective bulksuperconductors, the pressure was increased up to 0.2 MPa and,thereafter, heating was applied thereto below 80° C. for 6 hours andbelow 120° C. for 2 hours, thereby curing the resin.

An artificial through-hole (1 mm in diameter) was bored in therespective bulk superconductors impregnated with the epoxy resin, usinga drill. The through-hole was provided in the central part of therespective bulk superconductors, in the direction of the c-axis thereof.

Subsequently, the same treatment with the silane-based coupling agent asdescribed above was applied thereto, an aluminum bar (a soft wire-likebar 0.9 mm in diameter) was inserted into the artificial through-hole asbored, and an end of the aluminum bar, protruding into a bottom part ofthe respective bulk superconductors (on the side where the seed crystaldid not exist), was split into two parts to be brought into intimatecontact with the bottom surface of the respective bulk superconductors.

The respective bulk superconductors were preheated up to 150° C., aliquid metal having chemical composition of 53.9% Bi-25.9% Sn-20.2% Cdat 120° C. was poured so as to accumulate at the bottom of therespective bulk superconductors, and the pressure was reduced to6.7×10⁻² Pa in the vacuum tank to be subsequently increased up to 0.3MPa. Thereafter, the temperature was lowered down to normal temperature(20° C.), thereby solidifying the liquid metal.

Subsequently, the respective bulk superconductors with carbon fiberwound around the circumferential side face thereof were impregnated withresin by the same method as described above.

Next, the respective bulk superconductors were cooled down to 100K, amagnetic field with a magnetic flux density at 13 T was applied thereto,the respective bulk superconductors were further cooled down to 50K, andsubsequently, a magnetic field on the respective surfaces of the bulksuperconductors was measured by use of the Hall sensor device whilelowering the magnetic field from 13 T.

As a result, the specimens having a content of the Nd422 phase at 20%,30%, and 40%, trapped magnetic flux densities at a high value of 8 T, 11T, and 8 T, respectively.

On the other hand, when the same measurements as described above wereconducted on specimens wherein vacuum treatment with a low-melting metalwas not applied after providing an artificial hole, it was found thatafter the temperature of the bulk superconductors rose up to 55K in thecourse of lowering a magnetic field, there was a sudden increase intemperature up to 70K. It was confirmed that the trapped magnetic fieldsshowed magnetic flux density values close to 0 T.

As described in the foregoing, with all the specimens in whichimpregnation with the low-melting metal was applied after providing theartificial hole, relatively large trapped magnetic fields were obtainedas compared with the specimens to which such treatment was not applied.

Further, it was found by post-test observation with an opticalmicroscope that the interior of the artificial hole was filled with thelow-melting metal and internal microcracks in the vicinity of theartificial hole were also filled with the low-melting metal.

Example 4

Respective bulk materials comprising a YBa₂Cu₃O_(y) superconductor and aY₂BaCuO₅ phase dispersed therein, in an amount of 0, 10, 20, 30, and 40%by volume, respectively, with the addition of 10% by weight of Ag, wereprepared by the melt process.

Melting conditions were adopted such that YBa₂Cu₃O_(y) material with aYBa₂Cu₃O_(y) crystal on top as a seed crystal was cooled down to 1000°C. in 30 minutes after heating at 1050° C. for 20 minutes, andsubsequently, was further cooled down to 900° C. at a cooling rate of0.5° C./h.

Thereafter, oxygen annealing was applied thereto in an oxygen flow at400° C. under one atmospheric pressure for 250 hours.

Next, respective bulk superconductors were placed in a vacuum container,and the respective bulk superconductors were permeated with resin by thefollowing method of resin impregnation.

That is, first, in a preprocess stage, the respective bulksuperconductors were immersed in a silane-based coupling agent {R′ Si(OR)₃: R′ is an organic functional group, and OR is an inorganicfunctional group}, and were placed in a vacuum tank so as to be in acondition of reduced pressure at 6.7×10⁻² Pa, subsequently, reverting toa condition under atmospheric pressure. Then, the respective bulksuperconductors were put in a drying furnace to be dried.

Subsequently, bisphenol A epoxy resin, an aromatic polyamine, and asilane-based coupling agent, in a condition preheated up to 30° C., weremixed at a blending composition (weight ratio) of 100:32:1. Thereafter,the respective bulk superconductors were preheated up to 70° C., theresin was poured in such a way as to cover the respective bulksuperconductors, and the respective bulk superconductors were put in thevacuum tank where pressure was reduced to 6.7×10⁻² Pa to then bedeaerated. After sufficiently eliminating pores, the pressure wasincreased up to 0.2 MPa, and heating was applied thereto below 80° C.for 6 hours and below 120° C. for 2 hours, thereby curing the resin.

An artificial through-hole (1 mm in diameter) was bored in the bulksuperconductors, impregnated with the epoxy resin, using a drill. Thethrough-hole was provided in the central part of the respective bulksuperconductors, in the direction of the c-axis thereof.

Subsequently, the same treatment with the silane-based coupling agent asdescribed above was applied thereto, an aluminum bar (a soft wire-likebar 0.9 mm in diameter) inserted into the artificial through-hole asbored, and an end of the aluminum bar, protruding into a bottom part ofthe respective bulk superconductors (on the side where the seed crystalwas not on) split into two parts to be brought into intimate contactwith the bottom surface of the respective bulk superconductors.

The respective bulk superconductors were preheated up to 150° C., aliquid metal having a chemical composition of 57% Bi-17% Sn-26% In at100° C. was poured so as to accumulate at the bottom of the respectivebulk superconductors, and the pressure was reduced to 6.7×10⁻² Pa in thevacuum tank to be subsequently increased up to 0.3 MPa. Thereafter, thetemperature was lowered down to normal temperature (20° C.), therebysolidifying the liquid metal.

Subsequently, the respective bulk superconductors with carbon fiberwound around the circumferential side face thereof were impregnated withresin by the same method as described above.

Next, the respective bulk superconductors were cooled down to 100K, amagnetic field with a magnetic flux density at 16 T was applied thereto,the respective bulk superconductors were further cooled down to 30K, andsubsequently, a magnetic field on the respective surfaces of the bulksuperconductors was measured by use of the Hall sensor device whilelowering the magnetic field from 16 T.

As a result, the specimens having a content of a Y211 phase at 0, 10,20, 30, and 40%, trapped magnetic flux densities of 11 T, 12 T, 12 T, 15T, and 13 T, respectively.

On the other hand, when the same measurements as described above wereconducted on specimens wherein vacuum treatment with a low-melting metalwas not applied after providing the artificial hole, it was found thatafter the temperature of bulk superconductors rose up to 55K in thecourse of lowering the magnetic field, there was a sudden increase intemperature up to 70K. It was confirmed that the trapped magnetic fieldsshowed magnetic flux density values close to 0 T.

As described in the foregoing, with all the specimens wherein treatmentof impregnation with the low-melting metal was applied after providingthe artificial hole, relatively large trapped magnetic fields wereobtained as compared with the specimens to which such treatment was notapplied.

Further, it was found by post-test observation with a microscope thatthe space between the aluminum bar and the respective bulksuperconductors, inside the artificial hole, was filled with thelow-melting metal and internal microcracks in the vicinity of theartificial hole were also filled with the low-melting metal.

Example 5

Specimens of respective bulk materials comprising anSm_(0.9)Ba_(2.1)Cu₃O_(y) oxide superconductor and an Sm₂BaCuO₅ phase(Sm211 phase) dispersed therein, in an amount of 0, 10, 20, 30, and 40%by volume, respectively, with 15% by weight of Ag, added thereto, wereprepared by the melt process.

Melting conditions were adopted such that Sm_(0.9)Ba_(2.1)Cu₃O_(y)material with an SmBa₂Cu₃O_(y) phase therein as a seed crystal wascooled down to 990° C. in 20 minutes after heating at 1010° C. for 20minutes in “an atmosphere of a mixed gas of oxygen and argon with anoxygen partial pressure maintained at 1%”, and subsequently, was furthercooled down to 850° C. at a cooling rate of 0.5° C./h.

In the specimens without Sm 211, in a post-growth stage, microcrackswere observed although not by the naked eye.

Thereafter, oxygen annealing was applied to respective bulksuperconductors containing 10%, 20%, 30%, and 40% of the Sm211 phase,without any cracks being observed, in an oxygen flow at 350° C. underone atmosphere pressure for 200 hours.

Next, the respective bulk superconductors were placed in a vacuumcontainer, and were permeated with resin by the following method ofresin impregnation.

That is, in a preprocess stage, the respective bulk superconductors wereimmersed in a silane-based coupling agent {R′ Si (OR)₃: R′ is an organicfunctional group, and OR is an inorganic functional group}, and were putin a vacuum tank so as to be in a condition of a reduced pressure at6.7×10⁻² Pa, subsequently reverting to a condition under atmosphericpressure. Then, the respective bulk superconductors were put in a dryingfurnace to be dried.

Subsequently, bisphenol A epoxy resin, an aromatic polyamine, and asilane-based coupling agent, in a condition preheated up to 30° C.,respectively, were mixed at a blending composition (weight ratio) of100:32:1. Thereafter, the respective bulk superconductors were preheatedup to 70° C., the resin was poured in such a way as to cover therespective bulk superconductors, and the respective bulk superconductorswere put in the vacuum tank where the pressure was reduced to 6.7×10⁻²Pa to then be deaerated. After sufficiently eliminating pores, heatingwas applied thereto below 80° C. for 6 hours and below 120° C. for 2hours, thereby curing the resin.

Artificial through-holes (0.8 mm in diameter) were bored in therespective bulk superconductors and impregnated with the epoxy resin,using a drill. The through-hole was provided at three spots locatedbetween the center of the respective bulk superconductors, in thedirection of the c-axis thereof, and the periphery thereof.

Subsequently, an aluminum bar (a soft wire-like bar 0.7 mm in diameter)was inserted into the respective artificial through-holes as bored, andrespective ends of the aluminum bars were kept in such a condition asexposed to the outside.

The respective bulk superconductors were preheated up to 100° C., aliquid metal having chemical composition of 40% Bi-40% Pb-11.5% Sn-8.5%Cd also at 100° C. was poured so as to accumulate at the bottom of therespective bulk superconductors, and the pressure was reduced to6.7×10⁻² Pa in the vacuum tank to be subsequently increased up to 0.3MPa. Thereafter, the temperature was lowered down to normal temperature(20° C.), thereby solidifying the liquid metal.

Subsequently, the respective bulk superconductors with carbon fiberwound around the circumferential side face thereof were impregnated withresin by the same method as described above.

Next, the respective bulk superconductors were cooled down to 100K, amagnetic field with a magnetic flux density at 16 T was applied thereto,the respective bulk superconductors were further cooled down to 30K, andsubsequently, a magnetic field on the respective surfaces of the bulksuperconductors was measured by use of the temperature of the respectivebulk superconductors and the Hall sensor device while lowering themagnetic field from 16 T.

As a result, the specimens having a content of the Sm211 phase at 10%,20%, 30%, and 40%, trapped magnetic flux densities of 10 T, 13 T, 13 Tand 10 T, respectively.

On the other hand, when the same measurements as described above wereconducted on specimens in which vacuum treatment with a low-meltingmetal was not applied after providing artificial holes, it was foundthat the trapped magnetic fields of the specimens having a Sm211 phasecontent of 10%, 20%, 30%, and 40%, had magnetic flux densities of 1 T, 1T, 0.5 T and 0.5 T, respectively.

As described in the foregoing, with all the specimens wherein thetreatment of impregnation with the low-melting metal was applied afterproviding the artificial holes and installing the aluminum bar therein,relatively large trapped magnetic fields were obtained as compared withthe specimens to which such treatment was not applied.

Further, it was found by post-test observation with a microscope thatthe space between the aluminum bar and the respective bulksuperconductors, inside the respective artificial holes, was filled withthe low-melting metal and internal microcracks in the vicinity of therespective artificial holes were also filled with the low-melting metal.

Example 6

Specimens of bulk materials comprising a YBa₂Cu₃O_(y) superconductor anda Y₂BaCuO₅ phase dispersed therein, in an amount of 0, 10, 20, 30, and40% by volume, with 10% by weight of Ag, added thereto, were prepared bythe melt process.

Melting conditions were adopted such that YBa₂Cu₃O_(y) material wascooled down to 1000° C. in 30 minutes after heating at 1050° 0 for 20minutes, and subsequently, was further cooled down to 900° C. at acooling rate of 0.5° C./h after placing a YBa₂Cu₃O_(y) phase therein asa seed crystal.

After crystal growth, oxygen annealing was applied thereto in an oxygenflow at 400° C. under one atmosphere pressure for 250 hours.

Then, artificial through-holes (0.8 mm in diameter) were bored inrespective bulk superconductors, using a drill. The through-holes wereprovided at three spots located between the center of the respectivebulk superconductors, in the direction of the c-axis thereof, and theperiphery thereof.

Subsequently, an aluminum bar (a soft wire-like bar 0.7 mm in diameter)was inserted into the respective artificial through-holes as bored, andrespective ends of the aluminum bars were kept in such a condition as tobe exposed to the outside.

The respective bulk superconductors were immersed in a silane-basedcoupling agent {R′ Si (OR)₃: R′ is an organic functional group, and ORis an inorganic functional group} and were put in a vacuum tank so as tobe in a condition of reduced pressure at 6.7×10⁻² Pa, subsequently,reverting to a condition under atmospheric pressure. Then, therespective bulk superconductors were put in a drying furnace to bedried.

The respective bulk superconductors were preheated up to 100° C., aliquid metal having a chemical composition of 57% Bi-17% Sn-26% In alsoat 100° C. was poured so as to accumulate at the bottom of therespective bulk superconductors, and the pressure was reduced to6.7×10⁻² Pa in the vacuum tank to be subsequently increased up to 0.3MPa. Thereafter, the temperature was lowered down to normal temperature(20° C.), thereby solidifying the liquid metal.

Next, the respective bulk superconductors were cooled down to 100K, amagnetic field with a magnetic flux density at 13 T was applied thereto,the respective bulk superconductors were further cooled down to 50K, andsubsequently, a magnetic field on the respective surfaces of the bulksuperconductors was measured by use of the Hall sensor device whilelowering the magnetic field from 13 T.

As a result, the specimens having a Y211 phase content of 0, 10, 20, 30,and 40%, trapped magnetic flux densities of 5 T, 8 T, 7 T, and 5 T,respectively.

On the other hand, when the same measurements as described above wereconducted on specimens wherein vacuum treatment with a low-melting metalwas not applied after providing the artificial holes, it was found thatthe trapped magnetic fields of those specimens having a Y211 phasecontent of 20, 30, and 40%, showed magnetic flux density values of 1 T,2 T, and 1.5 T, respectively.

As described in the foregoing, with all the specimens wherein treatmentof impregnation with the low-melting metal was applied after providingthe artificial holes and installing the aluminum bar therein, relativelylarge trapped magnetic fields were obtained as compared with thespecimens to which such treatment was not applied.

Further, it was found by post-test observation with a microscope thatthe space between the aluminum bar and the respective bulksuperconductors, inside the respective artificial holes, was filled withthe low melting metal and internal microcracks in the vicinity of therespective artificial holes were also filled with the low-melting metal.

Further, it was confirmed that the mechanical strength was alsoconcurrently enhanced by applying the vacuum treatment with thelow-melting metal.

Thus, the present invention can provide a superconducting magnet made ofa high-temperature bulk superconductor which is capable of efficientlysecuring a high trapped magnetic field in a relatively short time andcan bring about very useful effects from the industrial viewpoint inthat there can be expected a great contribution made to enhancement inperformance of equipment to which the high-temperature bulksuperconductor is applied, for example, a magnetic levitation train,superconducting bearings for use in flywheel energy storage, a magneticseparation apparatus, and so forth.

What is claimed is:
 1. A process for producing a superconducting magnetwhich restrains a flux jump at the time of magnetizing in a highmagnetic field, comprising the steps of: providing a high-temperaturebulk superconductor material; forming an artificial hole in thehigh-temperature bulk superconductor material; disposing aheat-conducting metal material for restraining the heat flux jump at atleast portions of the high-temperature bulk superconductor materialwhere bonding of the heat-conducting metal material with a low meltingmetal material to be impregnated in the high-temperature bulksuperconductor material can be made; impregnating the high-temperaturebulk superconductor material with the low melting metal material ineither a reduced pressure or pressurized atmosphere so that at least theartificial hole is impregnated and filled with the low-melting metalmaterial; solidifying of the low-melting metal material and bonding thesolidified low-melting metal material with the heat-conducting metalmaterial; and magnetizing the high-temperature bulk superconductormaterial containing the solidified and bonded low-melting metal materialin an external magnetic field with a magnetic flux density in excess of10 T to provide the superconducting magnet.
 2. The process of claim 1,wherein the low-melting metal material has a melting point of no morethan 200° C.
 3. The process of claim 1, wherein the heat-conductingmetal material is aluminum.
 4. The process of claim 1, wherein thesuperconducting magnet has a trapped magnetic flux density of from 5-15T.
 5. The process of claim 1, wherein the high-temperature bulksuperconducting material comprises a YBa₂Cu₃O_(y) superconductor and aY₂BaCuO₅ phase dispersed therein and 6.5<y<7.2.
 6. The process of claim1, wherein the artificial hole extends throughout the thickness of thehigh-temperature bulk superconducting material.
 7. The process of claim1, wherein the low-melting metal material has a melting point of nogreater than 300° C.
 8. The process of claim 1, wherein theheat-conducting metal material is selected from the group consisting ofCu, Ag and Au.
 9. The process of claim 1, wherein a wire made of theheat-conducting metal material is disposed in the artificial hole priorto impregnating the high-temperature bulk superconductor material withthe low-melting metal material and the ends of the wire are split anddisposed outside the artificial hole.
 10. The process of claim 1,wherein the heat-conducting metal material is selected from the groupconsisting of Al, Cu, Ag and Au and the low-melting metal material has amelting point not higher than 200° C.
 11. The process of claim 1,wherein the artificial hole is a through-hole.
 12. The process of claim1, wherein the artificial hole is a bottomed hole.